The subject invention concerns a heat-exchanger roll and a method and an apparatus for the manufacture of heat-exchanger rolls.
In its operational condition, the heat-exchanger forms a rotating wheel, wherein the exchange of heat is obtained by rotating the wheel between flows of fluid of different temperatures so that said fluid flows are heated or cooled by the walls of the channels formed in the wheel.
Heat-exchangers of the type concerned herein are known since 1924. In the technical field to which the subject invention belongs, i.e. recovery of heat/cold with the aid of ventilation air, wheels of this kind began to be used to an increasing degree after the second World War. The energy crisis of 1975 has speeded up the use further.
In the beginning, the wheels were made of strips of asbestos. In the middle of the 1960s the use of webs of aluminium foil was initiated. The corrugated (pleated) and plane (straight) foils were joined together by means of epoxy or polyurethane glue. However, the problems of manufacturing this kind of wheels are considerable, in addition to which their strength and durability are inferior.
The problems arising in the manufacture of wheels of this kind are mainly concerned with the glue. It has to be applied very exactly on the crests of the pleats. In addition, the glue must not spread or be pulled out during the winding-on operation. After the winding-on operation the wheel must be transferred to an oven, wherein the glue is allowed to set. During this process the glue serves as a lubricant encouraging movement between the pleats and the plane foil, which makes the handling of the wheel delicate. During the setting process excess glue has a tendency to spread and block the channels to a larger or smaller extent. In addition, the glue may also be the cause of exzema, allergies and other similar serious illnesses which are difficult to remedy.
A small, often invisible, fault in the glue bond may easily cause the total collapse of the wheel. It is therefore necessary to test the wheels carefully for strength before they are installed.
However, this safety measure is not enough since the strength of the glue bond often deteriorates in some environments as the glue gradually decomposes. This has lead to a large number of wheel collapses, particularly of large wheels of diameter sizes of 3 meters or more, and of heavily loaded wheels. The costs of repair or exchange of such large-size wheels are exceptionally high.
The technical problems involved in obtaining long-term durability and strength of glue bonds in aluminium in moist invironments and the difficulty in solving these problems are well known to the artisans in the field. Various methods have been attempted to solve these problems.
The safest--but also the most expensive--way of solving the problem is to cut the wheel into segments, after the glueing operation, and to insert the segments in self-supporting frames. The method is very complicated and expensive. Another method uses 4 to 8 spokes which are inserted into channels milled into the two faces of the wheel to take the majority of the strain. This method is used predominantly in smaller wheels having a maximum diameter of about 1.5 to 2 meters.
A third method also uses 4 to 8 spokes which are hammered or drilled diametrically through the wheels after the wheel-glueing operation. This method is used generally by several manufacturers.
The spokes, however, reduce the through-flow area and complicate the manufacture. In addition, the long-term effect has not yet been tested.
The purpose of the subject invention is to eliminate the glueing operation completely while at the same tim e provide considerably more efficient exchange of heat than in heat-exchangers fitted with rolls of prior-art types.